Mental Math for Everyday Life
Ditch the phone calculator and build intuitive number sense. Learn the mental shortcuts that turn everyday tips, discounts, and ballpark calculations into second nature.
Like Duolingo, but for Mental Math for Everyday Life. Tomo turns the whole topic into a game you play five minutes a day, until it actually sticks.
A short one: 11 levels across 2 sections, about 22 minutes end to end, roughly 4 days at five minutes a day. It moves through Everyday Calculations in Your Head and Estimation and Sanity Checking. It starts from scratch.
Free forever · No credit card · iPhone & Android
Key ideas in Mental Math for Everyday Life
- The leftmost digits represent the largest place values and determine the scale of the answer immediately
- Pencil-and-paper math moves right-to-left to track carries, but mental math works better left-to-right to hold a running ballpark
- Adding the largest digits first tells you within seconds whether a total crosses a threshold like $100
- Front-end addition splits multi-digit numbers into tens and ones before adding
- You update a single running total in memory rather than holding two separate partial answers
- Adding tens first (50 + 20 = 70) creates a stable anchor before tacking on the ones
- Bridging up turns subtraction into finding the distance between two numbers by hopping forward
- The first step is hopping to the nearest multiple of ten (58 + 2 = 60)
- The second step is hopping from that clean ten to the target number (60 + 23 = 83), then adding the hops (2 + 23 = 25)
- Rounding an added number up to a friendly landmark means you added too much
- To balance the total, you must subtract the extra amount you added (94 − 1 = 93)
- Compensation requires adjusting the final total in the opposite direction of your initial bump
- Ten percent is found by shifting the decimal one place left, fifty percent by halving, and one percent by shifting two places left
- Complex percentages can be built by adding or subtracting combinations of 50%, 10%, and 1%
- X percent of Y is mathematically identical to Y percent of X because both equal (X × Y) / 100
- Flipping an awkward percentage with a friendly number (like 25%, which is simply one quarter) makes the calculation effortless
You've tried the other tabs
Thirty open tabs. Four facts you actually kept.
You watched. You nodded. By Sunday it was gone.
One answer, then back to scrolling.
Eight weeks. You meant to finish. You didn't.
Tomo gives Mental Math for Everyday Life the Duolingo treatment: levels, streaks, and quick quizzes that test what you just learned. That game loop is what the tabs above never had, so it's the one you actually finish.
Here's what playing it feels like
A real question from this course. Take your best guess.
Why do we add left-to-right in our heads when school taught us to write right-to-left?
Get it right to open this lesson and 10 more in the app.
Where Mental Math for Everyday Life takes you
- 1
Everyday Calculations in Your Head
- Calculating Left-to-Right in Your Head
- Cracking Percentages and Discounts
- 2
Estimation and Sanity Checking
- Friendly Numbers and Multiplication Shortcuts
- Fast Reality Checks and Ballpark Estimation
2 sections · 4 units · 11 levels. Built to play, not to enroll.
Tomo is in ChatGPT
Tomo is also a ChatGPT plugin: the same playable courses, built and played inside your chat.
Add Tomo to ChatGPT- What to ask
- “Make me a Tomo course on black holes.” “Turn this chat into a Tomo course.”
- What you get
- Quick questions with instant feedback, hearts and stars, ready to play in about a minute.
- Where it goes
- No sign-up to start. Connect your Tomo account and your streak carries on in the app.
You pick the voice
Mental Math for Everyday Life is taught in the Bestie style: your friend who just gets it. Want a different feel? In the app you can spin up the same topic in any of Tomo's teaching styles. Same facts, totally different vibe.
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Everyday Number Sense
Build an instinctive radar for whether real-world numbers make sense. Learn to spot misleading statistics, scale errors, and deceptive charts in headlines and daily life.
Start Mental Math for Everyday Life today.
Download Tomo, search Mental Math for Everyday Life, and play your first lesson in under a minute.